1. Field of the Invention
This invention relates generally to a method and apparatus for providing an output indication proportional to the moisture content of particulate material and, more particularly, but not by way of limitation, to a method and apparatus for providing an output indication proportional to the moisture content of particulate material wherein a probe drive signal having predetermined frequency and amplitude is applied to the particulate material and a current indicator signal proportional to the current applied to the particulate material is provided, the current indicator signal being proportional to the moisture content of the particulate material.
2. Description of the Prior Art
In the past, various methods and apparatus have been devised to provide indications of the moisture content of particulate materials. Although such prior art devices are generally classifiable as either resistive or capacitive measuring devices, other methods for estimating the moisture content of materials have been devised such as the radio wave absorption device represented by the U.S. Pat. No. 3,714,560 issued to Farr. Representative of the capacitive measuring tape devices is the circuit disclosed in U.S. Pat. No. 3,300,716 issued to Engert.
Within the general catagory of resistive measuring devices, the prior art devices may be further subdivided according to the type of signal applied to the sample material, i.e., AC or DC. Within the DC subdivision are the prior art devices represented by the following U.S. patents: U.S. Pat. No. 2,548,410 issued to Tyson; U.S. Pat. No. 2,755,438 issued to Cudmore; and U.S. Pat. No. 3,197,699 issued to Johansen. Within the AC subdivision are the prior art devices represented by the following U.S. patents: U.S. Pat. No. 2,759,149 issued to Hart; and U.S. Pat. No. 3,141,129 issued to Dietert. The following U.S. patents disclose prior art devices of both the AC and DC types: U.S. Pat. No. 2,862,304 issued to Estienne; and U.S. Pat. No. 3,331,020 issued to Farenkopf.
Related prior art probe apparatus is disclosed in U.S. Pat. No. 3,631,337 issued to MacKinney.